The present invention relates to a semiconductor device having an improved pattern and a method of forming the same as well as a photo-mask used in the method of forming the semiconductor device, and more particularly to a method of forming a pattern for capacitors of dynamic random access memories needed to be increased in capacity but in a limited occupied area, and a method of forming the same as well as a photo-mask.
The dynamic random access memory has memory cell arrays, each of which comprises a switching transistor and a capacitor. The requirement for an increase in the density of integration of the dynamic random access memory has been on the rise, whereby it has become important to obtain a required capacity in a limited or reduced occupied area of the capacitor. A stacked capacitor and a trench capacitor are examples of the proposed capacitors having a three-dimensional structure. The three-dimensional structure contributes to increase a surface area of the capacitor for allowing the capacitor to increase in capacity but in the limited or reduced occupied area.
FIG. 1 is a plan view illustrative of a conventional mask pattern to be used for patterning a storage electrode or a bottom electrode of a stacked capacitor. This mask pattern is for a positive type photo-resist. Rectangular-shaped opaque patterns 100 are aligned in matrix over the photo-mask, wherein the rectangular-shaped opaque patterns 100 do shield the ray. Positions of the rectangular-shaped opaque patterns 100 correspond to positions where the storage electrodes are intended to be formed. This mask pattern is used to carry out an exposure process under such conditions as to prevent adjacent rectangular-shaped opaque patterns 100 from being in contact with each other. Therefore, the photo-resist film is subjected to the exposure and subsequent development to form a photo-resist pattern. This photo-resist pattern is used as a mask for patterning a base conductive film to form the storage electrode. Circle-shaped broken lines 101 represent capacitive contact patterns.
The above conventional mask pattern has the following problem. FIG. 2 is a plan view illustrative of a photo-resist pattern formed by a photo-lithography using the photo mask pattern shown in FIG. 1. Even though the rectangular-shaped opaque patterns 100 are sharply rectangular shaped, an elliptically shaped photo-resist pattern 102 as shown in FIG. 2 is formed by a photo-lithography using the photo mask pattern of FIG. 1 due to an optical proximity effect. If a micro-pattern size is close to a limitation of the resolving power of the exposure system, then the resist pattern 102 formed by a photo-lithography using the photo mask pattern sharply rectangular shaped has rounded corners. This means that the resist pattern is different in shape from the photo-mask pattern due to the optical proximity effect, particularly if the pattern size is close to the limitation of the resolving power of the exposure system. The corners of the resist pattern 102 are rounded. This means that the actual area of the resist pattern 102 is smaller than the intended area thereof. This results in that the actual surface area of the capacitor is smaller than the intended area thereof, whereby the actual capacity of the capacitor is lower than the intended capacity of the capacitor. FIG. 3 is a plan view illustrative of a photo-resist pattern formed by a photo-lithography using the photo mask pattern shown in FIG. 1, wherein the size of the photo-resist pattern 103 is close to the limitation of the resolving power of the exposure system. If the size of the photo-resist pattern 103 is close to the limitation of the resolving power of the exposure system, then the optical proximity effect is more remarkable, whereby the shape of the resist pattern is closer to circular and the area of the resist pattern is more reduced. This results in that the actual area of the obtained capacitor is much smaller than the intended area of the ideal capacitor. Even if each corner of the rectangular-shaped opaque pattern 100 extends outwardly for the purpose of compensation of the optical proximity effect, then the scaling down of the pattern makes it difficult to compensate for the deformation of the photo-resist pattern.
The dynamic random access memory having the stacked capacitor is isolated into a capacitor under bit-line structure and a capacitor over bit-line structure. In the capacitor under bit-line structure, the capacitor is placed under the bit-line. In the capacitor over bit-line structure, the capacitor is placed over the bit-line. Particularly, in the capacitor under bit-line structure, it is essential to reduce the size of the pattern of the storage electrode for the purpose of securing a sufficient margin between the bit-contact and the storage electrode, resulting in further reduction in capacity.
In the above circumstances, it had been required to develop a novel semiconductor device such as a dynamic random access memory having capacitors with a large capacity but a limited or reduced occupied area and a method of forming the same as well as a photo-mask to be used therein, which are, however, free from the above problem.
Accordingly, it is an object of the present invention to provide a novel semiconductor device such as a dynamic random access memory having capacitors with a large capacity but a limited or reduced occupied area free from the above problems.
It is a further object of the present invention to provide a novel method of forming a semiconductor device such as a dynamic random access memory having capacitors with a large capacity but a limited or reduced occupied area.
It is a still further object of the present invention to provide a novel photo-mask to be used for forming a capacitor having a large capacity but a limited or reduced occupied area in a semiconductor device
The first present invention provides a semiconductor device having at least a pattern which is defined by a non-straight line.
The second present invention also provides a resist pattern having at least a pattern which is defined by a non-straight line.
The third present invention provides a mask to be used for an exposure in a lithography process, the mask having inverted patterns comprising transmission regions which are positioned at a circumference of each of intended patterns of a resist film.
The fourth present invention provides a method of forming a device pattern of a semiconductor device. The method comprises the steps of: carrying out an over-exposure to a resist film with the use of a mask which has inverted patterns comprising transmission regions which are positioned about a circumference of each of intended patterns of a resist film; carrying out a development of the resist film to form a resist pattern having the intended patterns; and forming a device pattern of a semiconductor device by use of the resist pattern.
The above and other objects, features and advantages of the present invention will be apparent from the following descriptions.